Fuse plug



April 25, 1950 F. LOPORTO 2,505,193

FUSE PLUG Filed Feb. 8, 1946 Patented Apr. 25, 1950 UNITED STATES PATENTOFFICE FUSE PLUG Frank Lopolto, Cicero, lll.

Application February 8, 1946, Serial No. 648,323

1 Claim. (Cl. 20G- 113) This invention relates to protective devices forelectrical circuits of the type which include a current carryingconductor adapted to be ruptured when heated by the overloading of thecircuit.

One object of the invention is to provide a, new and improved fuse plugin which a slender iliament of mercury is employed as one of theconductors, said mercury being overheated and expelled from its currentconducting position by an overload in the circuit but being retainedvwithin the plug so that it is adapted to be replaced in conductingposition without unsealing the plug or otherwise altering its structure.

Another object oi the invention is to provide a fuse plug in which a.quantity of mercury is employed as the current conductor sensitive tooverload and in which the displacement of said conductor from its normalposition serves to close an alarm circuit for indicating the conditionof the principal circuit in which the plug is contained.

It is also an object of the invention to provide a new and improved fuseplug of the type employing a liquid current carrying medium which isdisplaced from its normal current carrying position by an overload inthe circuit, said plug comprising a substantially transparent bodythrough which the displaced liquid is readily visible.

A further object of the invention is to provide equipment for protectinga, plurality of circuits including a new and improved fuse plug of thetype employing a liquid current carrying medium Which is displaced fromits normal current carrying position by an overload in the circuit, saidplug including a contact element positioned in the body of the plug tocontact the displaced liquid medium and to be connected therethroughwith one side f a feed circuit, said element extending outside the bodyof the plug so that by means of a signal device and test wire connectedto the other side of the circuit any such plug may be tested withoutremoval from its mounting for determining the circuit in which theoverload occurred.

Other objects and advantages of the invention will appear from thefollowing description taken in connection with the drawings, in which:

Fig. 1 is an axial sectional view showing a fuse plug embodying thisinvention, with a wiring diagram therefor.

Fig. 2 is a face view of a panel board having installed thereon aplurality oi fuse plugs similar to that shown in Fig. l, with anindicator lamp for each plug;

2 a modiiied form of the invention, with its wiring diagram.

Fig. 4 is a face view of a panel board provided with a plurality of fuseplugs like that shown in Fig. 3 and with a single indicator lamp andmeans for connecting it alternatively to any of the fuse plugs;

Fig. 5 is an axial sectional view of a fuse plug embodying thisinvention with an individual indicator lamp mounted directly on theplug, and a wiring diagram.

Fig. 6 is a transverse section taken as indicated at line 6-6 on Fig. 5.

In the form shown in Fig. 1, the fuse plug embodying this invention isprovided with a body I6 which is preferably of transparent material,such as glass or synthetic plastic, and which is formed with an axiallydisposed chamber I2 communicating with an axial bore I4 which isslightly larger than the chamber and in which there is inserted abushing I6 o1' conducting material such as brass or copper. The bushinghas a slender axial channel I8 which connects with a similar channel 2liin a plug 22 of insulating 26 material, said plug being tted into arecess in Fig. 3 is an elevation partly in section showing 55 the lowerend of the conducting bushing I6 and extending through a plate or washer24 of conducting material. Said plate 24 contacts the threaded metallicshell 26 of the plug and said shell 26 is anchored to the body I 0 inany convenient manner.

The plate or washer 24 is retained in position by means of an insulatingcap 28 which is held in place by the overlapping ange 3,0 of the shell26 and which carries the center contact element 32 disposed axially inthe cap 26 and engaged with the end of the insulating plug 22. 'Iheconducting plate 24 engages the lower end portion of the conductingbushing I6 which encircles the insulating plug 22. A small quantity ofliquid current conducting material 34. preferably mercury, normallyoccupies the axial channel 20 in the insulating plug 22 and extends intothe axial channel I8 of the conductor I6. Thus when the fuse plug isscrewed into a socket connected in the circuit to be protected. thecenter contact 32 of the plug engages the center contact of the socket,and the shell 26 engages the threaded shell of the socket. The circuitis completed by the column or filament of mercury 34 which engages thecenter contact 32 and connects it with the conductor bushing I6, whilethe latter is connected by the plate 24 with the shell 26.

The upper or outer end of the conducting bushing I6 is formed with aninverted conical recess 36 communicating with the bore or channel I6.

In the event of a short circuit or overload, the momentary overheatingof the mercury 88 causes a portion of 1t to vaporize and expand rapidly,forcing the entire column into the chamber I2 of the body I8. Thisbreaks the circuit and the mercury instantly cools and falls back intothe recess .or cup 88 into the position indicated in dotted lines at 88;but the restricted character of the channel I8 prevents the mercury fromflowing by gravity into said channel and reestablishlng the circuit. Ifthe fuse plug be removed from the socket and shaken sharply, the mercuryis readily forced back into the restricted channels I8 and 28, thusrenewing the plug for further service, and such renewal can be repeatedindefinitely.

By reason of the fact that the body I8 is made of transparent material,an installation of fuse plugs of this type can be easily and readilyinspected without removal from their supporting sockets, and if any ofthe plugs has blown" as a result of a short circuit or overload, thisfact will be readily apparent because the globule of mercury resting inthe chamber I2 if the plug is in horizontal position, or in the cup 88at 88 if the plug is installed vertically, can be seen through thetransparent body I8.

The present invention provides additional means for readily anddefinitely identifying the plug which has been "blown by a shortcircuit, and this means may be embodied in the fuse plug whether it bemade of transparent or of opaque material, such as porcelain. Said meansincludes a conductorl I8 which is permanently embedded in the body I8 soas to extend into the chamber I2 and toward the recess 88, as shown inFig. 1. In the event of an overload or short circuit, the mercuryglobule formed at 88 will extend into contact with the conductor 88.Outside the body I Ii the conductor is threaded so as to serve as abinding po'st and is provided with a knurled nut 82 for clamping one endof conductor wire 88. This wire is connected to one terminal of a sisnallamp 88, while the other terminal of the lamp extends to the line wireor feed wire L1, as diagrammatically shown in Fig. l. The lamp or otherappliance in the circuit protected by the fuse is shown at A, connectedbetween line wires L1 and L with the fuse in series with the element A.When the fuse is blown, a new circuit is established from Irl throughlamp 58, conductor 88, conductor 88. mercury 88, bushing I8, plate 28,and shell 28 which is already connected to line wire L. The lighting ofthe lamp 88 thus indicates that the fuse has fimctioned. ^f As sho'wn inFig. 2, each section of the panel board 88 includes a fuse plug body I8and a corresponding indlcamr lamp nto which a wire u extends. Thus,whenever a short circuit causes the mercury 8l in a fuse plug to'beexpelled from its normal position in the channels I8 and .28 to itsposition at 38 in the recess 88, it will complete the circuit of thecorresponding lamp 88 which will glow as a signal to identify the fuseplug requiring attention for renewal.

Fig. 3 illustrates a slight modiiication of the fuse plug structure andFig. 4 shows a modified arrangement of the panel board. In Fig. 8 thefunctioning-portions of the fuse device as such may be understood assimilar to those of Fig. 1 already described, but instead of theconductor 48 with its binding post 42 the body portion Ila of the plugshown in Fig. 3 carries a conductor 88 having merely a smoothly roundedhead 82 conductor 88 carries a single indicator lamp 18 and a single,preferably flexible, conductor 88 hangs from its connection to thesocket of the lamp 18 in a position in which its contact terminal 88 isnormally clear of all the fuse plug bodies I8a on the board. In theevent of an overload or short circuit causing one of the plugs to blow,the defective circuit can be promptly identified by swinging theconductor 88 so as to bring its terminal 88 selectively into contactwith the exposed contact heads 82 of the several fuse plugs until suchengagement causes lighting of the signal lamp 18. As a matter ofconvenience, the fuse plugs are shown arranged on the panel board 88 inan arc concentric with the axis of the lamp 18.

Figures 5 and 6 illustrate a further modification of the fuse plug inwhich it is arranged to carry its own signal lamp. The body IIIb may beof transparent or opaque insulating material, and the internal portionsof the fuse device itself are similar to those shown in Fig. l and areidentified by corresponding numerals. The outer end of the plug body IUbis shown surmounted by a washer 12 which may be of nbre or likematerial, and serves to seat the in-turned base flange of a metallicsocket 18, the base portion of the socket being bent over and enclosingan insulating disc 'I8 through which a bolt 18 extends into the body I8bof the fuse plug. The threaded end of the bolt extends into the chamberI2 in the plug body and is secured therein by a nut 88 which thusclampsithe socket 18 in position on the outer end of the body I8b. Thehead of the bolt 18 serves as a center contact for the small indicatorlamp 82 which is supported in the socket 'I8. The socket itself isprovided vwith a lug 88, and a 88 extends therefrom to the line wire L1.p

With this arrangement, it will be evident that as long as the filamentor column of mercury 88 functions to complete the circuit for the lampor other device at A through the contact element 82 and the conductingbushing I8, the lamp 82 will not be energized, but that in the event ofa short circuit which causes the mercury to leave the bores I8 and 28and to settle in the cup or recess 88, the globule of mercury thusformed at 88 will provide a connection between the line wire L, shell28, plate 28, bushing I8 and the bolt 18 which is in contact with thecenter of the base of the indicator lamp 82. The other side of thecircuit for the lamp 82 is already completed through the socket 18, lug88, and conductor 88, leading to line wire L1. Thus in any panel boardcontaining a considerable number of fuse plugs oi'` this type, thefailure of any circuit will be indicated immediately by the glowing ofthe indicator lamp 82 on the plug which has been affected. The plug thenmay be removed and shaken down to restore the mercury to the channels I8and 28 and thus renew the plug for further service. If the defectivecircuit is known to be yagain in safe condition, the plug will bereplaced at once in its socket to resume service.

While I have shown and described herein certain structure embodying myinvention and illustrative thereof, it is to be understood that theinvention is not limited thereto or thereby but'embraces all changes andmodifications in its various features which may come within the scope ofthe appended claim.

I claim:

A fuse including an insulating, centrally aperexposed outside the bodyI8a. The panel board 'IISA tured body, a conducting bushing seatedtherein,

somos closing the outer portion of the aperture and at its outer end ushwith the end of the body, an insulating plug socketed in the conductingbushing and extending beyond the end of the body, a conducting washerencircling the plug, engaging the end of the body and the end of theconducting bushing, an insulating cap socketed to contain the outer endof the insulating bushing and to engage the outer face of the conductingwasher, a threaded conducting shell encircling the fuse body, engagingthe washer throughout substantially its entire periphery and ilanged tooverlie the insulating cap and hold it iirmly against the washer, aconducting pin extending axially through the insulating cap, theinsulating plug and conducting bushing being each centrally apertux'edto dene an aligned capillary tube extending from the conducting pin tothe inner end of the conducting bushing, the capillary tube beingadapted to contain a liquid conn The following references are of recordin the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,531,756 Roach Mar. 31, 19251,705,678 Pierce Mar. 19, 1929 1,813,344 Gilbert July 7, 1931 1,958,977Riv-ers May '15, 1934 2,038,970 Tessier Apr. 23, 1936 2,059,681 CrimminsNov. 3, 1936 2,060,819 McHugh Nov. 17, 1936 2,063,813 Kellendorfer Dec.8, 1936 2,079,462 McHugh May 4, 1937 2,097,406 Jenkins Oct. 26, 1937

